Electrochemically deposited 2D nanowalls of calcium phosphate-PDDA on a glassy carbon electrode and their applications in biosensing

A novel calcium phosphate (CaP)-poly[diallyidimethylammonium chloride] (PDDA) composite film with two-dimensional (2D) nanostructure was first constructed on glassy carbon electrode (GCE) via a simply one-step cathodic electrodeposition method at room temperature. X-ray photoelectron spectroscopy, X-ray powder diffraction, scanning electronic microscopy, and electrochemical impedance spectroscopy were used to characterize the composite film. The experimental results demonstrated that PDDA plays an important role in the formation of nanowall-like morphologies. The effects of the percentage of PDDA and the deposition time on the film growth were investigated. The composite film is favorable for protein immobilization with many specific properties, such as nontoxicity, high specific surface area, large specific cell-volume, and sufficiently functional groups for attaching protein. Hemoglobin (Hb) immobilized on such a film showed a pair of stable and well-defined peaks at -0.403 and -0.303 V at the scan rate of 100 mV/s in phosphate buffer solution (pH 7.0). Electrochemical parameters such as the average surface coverage (Gamma) and the surface electron-transfer rate constant (k(s)) were estimated to be 3.66 x 10(-11) mol/cm(2) and 1.0 s(-1). The immobilized Hb gave excellent electrocatalytic performance to the reduction of O-2, HO2, and NO2-. Compared with other methods, this strategy provides a simple and efficient approach to prepare the functionalized composite film for immobilizing proteins. The resulting film has potential use in the fabrication of the third generation biosensors.